Atherosclerosis is the principal cause of heart attacks and strokes. It has been reported that about 50% of all deaths in the United States, Europe and Japan are due to atherosclerosis. Atherosclerotic lesions in the arterial wall characterize atherosclerosis. Cholesteryl esters (CE) are present in these atherosclerotic lesions. Low density lipoprotein (LDL) has been shown to be the major carrier of plasma CE, and has been implicated as the agent by which CE enter the atherosclerotic lesions.
Scattered groups of lipid-filled macrophages, called foam cells, are the first visible signs of atherosclerosis and are described as type I lesions. These macrophages are reported to contain CE derived from LDL. The macrophages recognize oxidized LDL, but not native LDL, and become foam cells by phagocytosing oxidized LDL. Larger, more organized collections of foam cells, fatty streaks, represent type II lesions. These lesions further develop into complex lesions called plaques, which can result in impeding the flow of blood in the artery.
It is widely believed that accumulation of LDL in the artery depends on the presence of functionally modified endothelial cells in the arterial wall. It has been reported in animal models of atherosclerosis that LDL, both native LDL and methylated LDL, accumulates focally and irreversibly only at the edges of regenerating endothelial islands in aortic lesions, where functionally modified endothelial cells are present, but not in the centers of these islands where endothelial regeneration is completed. Similarly, LDL accumulates in human atherosclerotic lesions. The mechanism by which the LDL accumulates focally and irreversibly in arterial lesions has not heretofore been understood.